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Average watts question

532woodchuck

532woodchuck

Member
Dec 16, 2013
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Hello everybody, I have a friend that run an RCI 2995 into an x-force straight 8. And the radio itself will produce 50w. avg on am and 200pep with a 10 Watt carrier. On ssb it does 150 avg and 200 pep. Now we turn the amp on and have a 500 watt carrier that swings back to 250 watts on avg on am but forward to 1500 pep now on ssb it will do 800 avg and 1500 pep? We've used a bird 43p and a Daiwa 801 and both are showing the same.

I told him it should do about 800 avg on am cause mine does, could it be in the radio tune? The SWR on the (2) antennas are 1.2:1/1.6:1 and very only slightly in readings.
Thanks, Woodchuck
 

That 'swinging backwards' is a very good indication that the amplifier is being over-driven, so drop the drive until it quits. It deals with 'duty-cycle' of the amplifying devices with the particular mode of operation, which usually means an early grave and terrible audio. That's not 'opinion', it's fact. There ain't no free lunch so it's up to you.
I would very much suggest that you not use that 'Pep' meter when dealing with AM. It doesn't tell you anything practical/useful, it just means bigger 'feel good' numbers and leads to misunderstandings about what you are measuring.
Have fun...
- 'Doc
 
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W5LZ said:
I would very much suggest that you not use that 'Pep' meter when dealing with AM. It doesn't tell you anything practical/useful, it just means bigger 'feel good' numbers and leads to misunderstandings about what you are measuring.
Have fun...
- 'Doc
Click to expand...
Why isn't the peak envelope important to an AM signal?
 
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532woodchuck said:
Hello everybody, I have a friend that run an RCI 2995 into an x-force straight 8. And the radio itself will produce 50w. avg on am and 200pep with a 10 Watt carrier. On ssb it does 150 avg and 200 pep. Now we turn the amp on and have a 500 watt carrier that swings back to 250 watts on avg on am but forward to 1500 pep now on ssb it will do 800 avg and 1500 pep? We've used a bird 43p and a Daiwa 801 and both are showing the same.

I told him it should do about 800 avg on am cause mine does, could it be in the radio tune? The SWR on the (2) antennas are 1.2:1/1.6:1 and very only slightly in readings.
Thanks, Woodchuck
Click to expand...
I see a couple fundamental issues here actually.

If you are driving 200 peak watts into an 8 pill and only getting 1500 peak watts out, there is a problem. Do you have enough DC power? Because that's less than 9dB of gain from transistors that are capable of 13-15dB. I don't run but 100w/pill, but I know people get 200w/pill everyday, so something is wrong.

Also, your SSB average numbers are way high, average SSB power should be in the neighborhood of 10-20% of peak power ........... depending on voice, processing, compression etc. So to me, such high average SSB numbers means IMD or a bad meter.

So if you work all that backwards a little, your 1500pep SSB/AM numbers should be no more than a 375w AM carrier and 550w or so average forward swing on peaks. SSB average power should be in the neighborhood of 300w.

ASSUMING for have enough DC power, I wouldn't think that it would take much more than 75-80w peak to drive that 8 pill to it's full potential. You're getting way up into gain compression and saturation causing IMD compounded by using an antenna vs a dummy load.

That's my best guess.
 
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"Why isn't the peak envelope important to an AM signal?"
Because it doesn't/can't tell you anything through direct manipulation about what's happening. It requires another 'stage' of conversion of numbers to provide useful information. It basically complicates things unnecessarily and only provides bigger 'feel good' numbers, makes you think more is happening than really is. And how do you know that you used the same conversion factor when changing from Avg to Pep power?
If you fill a bucket with water and dip it out one cup at a time you'll come up with one number. If you empty that bucket with a shot glass instead of a cup, that number will be bigger. It certainly doesn't mean there's more watter when you use a shot glass! That's a 'feel good' number. That 375 watts of AM is the equivalent of 1000 watts of SSB, right? 'Feel good' numbers...
- 'Doc
 
W5LZ said:
"Why isn't the peak envelope important to an AM signal?"
Because it doesn't/can't tell you anything through direct manipulation about what's happening. It requires another 'stage' of conversion of numbers to provide useful information. It basically complicates things unnecessarily and only provides bigger 'feel good' numbers, makes you think more is happening than really is. And how do you know that you used the same conversion factor when changing from Avg to Pep power?
If you fill a bucket with water and dip it out one cup at a time you'll come up with one number. If you empty that bucket with a shot glass instead of a cup, that number will be bigger. It certainly doesn't mean there's more watter when you use a shot glass! That's a 'feel good' number. That 375 watts of AM is the equivalent of 1000 watts of SSB, right? 'Feel good' numbers...
- 'Doc
Click to expand...
Short of a scope, how else can you determine if you are fully modulating the carrier?
 
Easy. Know the power level of the carrier. The applied modulation has to be the same level to fully 'modulate' that carrier. When the applied modulation power equals the carrier power then you have 100% modulation. It isn't exactly that 'simple' but it's close enough not to make any significant difference at all.
- 'Doc
 
W5LZ said:
Easy. Know the power level of the carrier. The applied modulation has to be the same level to fully 'modulate' that carrier. When the applied modulation power equals the carrier power then you have 100% modulation. It isn't exactly that 'simple' but it's close enough not to make any significant difference at all.
- 'Doc
Click to expand...
I'm not even sure what you are saying there, but this has been beat to death already. A good peak reading meter with an active metering circuit is an important tool for AM/SSB operators alike.
 
"I'm not even sure what you are saying there,"
And that's the problem. What I said is the definition of 'modulation percentage'. I would suggest learning what you can and proving me wrong... or right?
- 'Doc
 
W5LZ said:
Easy. Know the power level of the carrier. The applied modulation has to be the same level to fully 'modulate' that carrier. When the applied modulation power equals the carrier power then you have 100% modulation. It isn't exactly that 'simple' but it's close enough not to make any significant difference at all.
- 'Doc
Click to expand...
The average modulating power is only 50% of the average carrier power, 25% in each of the sidebands. So an undistorted sine wave will increase the average carrier power by 150%, but we don't talk in an undistorted sine wave and a peak/hold meter will capture the peak envelope while an average meter will just lazily hang around the carrier power.

So no, I'm don't know what you mean by saying the modulation power equals the carrier power.

I stand by my position that a peak meter is a valuable tool for AM operation. In fact, I recently read an article claiming that an active (not passive) peak/hold meter did a better job at capturing peaks than an oscilloscope.
 
I stumbled across this today if anyone is interested ......
 

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Export radios with dual finals or "pills" don't drive amps as well as lower output single final radios.
My dual final General LEE swings to 10 watts average on a Bird 43 and to 40 watts peak.
My lightly tuned Uniden Grant XL swings to 20 watts peak and modulates a 2x4 amp to 900 watts on a Bird 43P........My General LEE with double the drive swings the amp to 700 watts. Both radios sound impressive but the GL falls flat when driving any amp.
No one has explained it but it happens to everyone of our club members who runs an export into an amp.
 
This has been beat to death on every cb forum. But here's my angle. I don't and never owned a peak bird.
When the bird has a little wiggle you should be close to 100%. This is confirmed by the scope.
Doesn't mean it sounds good, but it's a start.
 

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